In order to reduce fuel consumption and man-hours in soil working, agricultural implement frames are often equipped with several lateral rows of tillage tools at forward, median and rear positions. When tillage tools are thus arrayed, it is necessary for the implement frame to be level in the soil working position to ensure uniform penetration of the tools from front to back and in the transport position to prevent undesired digging in of the tools when traveling over uneven ground. There are many arrangements in the prior art for leveling of clevis hitch connected agricultural implement frames. The simplest frame leveling arrangements from a functional standpoint are those which are strictly manual, wherein the pitch or angular orientation of the frame about a lateral axis is manually adjusted either in the lowered soil working position of the frame or in the raised transport position of the frame. However, such manual adjustments can be laborious, time-consuming and hazardous depending on the particular mechanism employed. Therefore, automatic or self-leveling arrangements which maintain or substantially maintain the pitch of the frame as it is converted between working and transport positions are preferred.
Although some frames are leveled by hydraulic means, the majority are leveled by mechanical means. Agricultural frames which are not supported entirely by the associated tractor are usually supported by tires which are arranged in a lateral line across the frame, such that in the transport position the frame is a semi-trailer. The mechanical leveling mechanisms transfer the motion of the frame lift mechanism in reverse sense or direction to the hitch member. Since the hitch member is fixed vertically by connection to the tractor, the frame front end reacts against the hitch to maintain the pitch of the frame. For example, in lifting the frame to the transport position, the frame lifting motion is transmitted to the hitch member as a downward force. Since the hitch member cannot move vertically, the force is transmitted back to the front end of the frame to lift same as the rest of the frame is lifted. Self-leveling of the frame during lowering to the working position occurs according to the same principles. There are many mechanisms in the prior art for transferring the lifting and lowering forces from a lift mechanism of a frame to the hitch member for frame leveling purposes. Such leveling mechanisms tend to be mechanically complex, involving many links, levers, pivots, and the like. Multitudinous mechanical parts entail higher manufacturing costs and require greater expenditures of time for periodic inspection and maintenance. In addition to automatic leveling of the frame as its height above ground is changed, leveling arrangements often include an adjustable member for adjusting the pitch angle of the frame in one or more positions of the frame. Many such pitch adjustment mechanisms are so positioned on the frame that an operator must risk life and limb to adjust the pitch of the frame. For example, on a frame wherein the pitch is adjusted by a telescoping link, the frame is lifted to the transport position by the lift mechanism, an operator climbs onto the frame and removes a pin from the telescoping link and, as the lift mechanism is slowly operated, the operator guides the telescoping members to the proper set of apertures and replaces the pin. One common mechanical component of frame leveling mechanisms is the bell crank. However, all bell cranks in known use on frame leveling mechanisms are rigid; that is, the angular relationship between the arms is fixed.